• Journal of Mechanical Science and Technology
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• v.14 no.12
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• pp.1365-1375
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• 2000

Two phase flows have been numerically calculated to analyze plume characteristics and liquid circulation in gas injection through a porous plug. The Eulerian approach has been for formulation of both the continuous and dispersed phases. The turbulence in the liquid phase has been modeled using the standard $textsc{k}$-$\varepsilon$ turbulence model. The interphase friction coefficient has been calculated using correlations available in the literature. The turbulent dispersion of the phase has been modeled by the "dispersion Prand시 number". The predicted mean flows is compared well with the experimental data. The plume region area and the axial velocities are increased with the gas flow rate and with the decrease in the inlet area. The turbulent intensity also shows the same trend. Also, the space-averaged turbulent kinetic energy for various gas flow rates and inlet areas has been obtained. The results are of interest in the design and operation of a wide variety of materials and chemical processing operations.

• 한국전산유체공학회:학술대회논문집
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• 1997.10a
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• pp.120-125
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• 1997

In the present work the influence of various physical parameters on the two-phase flow behavior in a self-heated porous medium has been studied using a numerical model, that is, the effects of heat generation rate, of porosity, of particle size, and of system pressure on the dryout process. To analyze the effect of these parameters, the variation of both liquid volumetric fraction (i.e., liquid saturation) and liquid axial velocity is evaluated at the steady state or at the onset of a first boiled-out region. The analysis of computational results indicate that a qualitative tendency exists between the parameters such as heat generation rate, porosity, effective particle diameter and the temporal development of the liquid volumetric fraction field up to dryout. In addition to these parameters, a variation of fluid properties such as phase density, phase viscosity due to a change of system pressure can be used for gaining insight into the nature of two-phase flow behavior up to dryout.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.11
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• pp.1925-1930
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• 2016

Fuel cell power generation system, unlike conventional energy sources, converts chemical energy into electrical energy through electrochemical reaction of hydrogen and oxygen. This paper presents the control of interleaved multi-phase boost converter as the feasibility study on small-scale prototype electric railway vehicle application using fuel cell generation system. PSIM simulation program is to be used to implement the modeling of the electrical fuelcell as well as traction motor control with interleaved multi-phase boost converter. Comparing the input current ripple rate, two-phase interleaved boost converter is less than the boost converter. But the more multi-phase not less proportional to the ripple factor. we confirmed that the amplitude of the input current ripple rate of converter depend on duty ratio.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.54 no.1
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• pp.47-53
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• 2005

Most of the loads in industrial power distribution systems are balanced and connected to three power systems. However, in the user power distribution systems, most of the loads are single & three phase and unbalanced, generating voltage unbalance. Voltage unbalance factor is mainly affected by load system rather than stable power system. Unbalanced voltage will draw a highly unbalanced current. As a result, the three-phase currents may differ considerably, thus resulting in an increased temperature rise in the machine. This paper presents a scheme on the characteristics of voltage and current unbalance factor under the load variation at the three phase 4-wire system. Load unbalance factor is measured by the power quality measurement apparatus and compared by the current unbalance factor. Two methods are indicated similar results. The voltage unbalance factor of the three-phase 4-wire system is approved by the field measurement. Each phase has an impedance each other by the unbalanced operation pattern and give rise to voltage unbalance.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.36 no.2
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• pp.80-87
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• 1987

This paper describes a new approach to control the two-phase servomotor driven with microprocessor based inverter. Conventional 6-step driving system has some shortcomings such as vibration and loss caused by the harmonic voltage. An attempt has been made to eliminate the harmonic content of output waveform by PWM technique and to simplify the control system by phase control method. In realizing the phase control by PWM technique proposed by this paper, control circuit and algorithm has been suggested. The proposed method has been applied to the speed control system with PI controller to confirm the adaptation of the servo system and experimental results has been compared with the computer simulation.

• Macromolecular Research
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• v.11 no.1
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• pp.53-61
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• 2003

A molecular-thermodynamic model is developed for the salt-induced protein precipitation. The protein molecules interact through four intermolecular potentials. An equation of state is derived based on the statistical mechanical perturbation theory with the modified Chiew's equation for the fluid phase, Young's equation for the solid phase as the reference system and a perturbation based on the protein-protein effective two body potential. The equation of state provides an expression for the chemical potential of the protein. In a single protein system, the phase separation is represented by fluid-fluid equilibria. The precipitation behaviors are simulated with the partition coefficient at various salt concentrations and degree of pre-aggregation effect for the protein particles. In a binary protein system, we regard the system as a fluid-solid phase equilibrium. At equilibrium, we compute the reduced osmotic pressure-composition diagram in the diverse protein size difference and salt concentrations.

• Journal of Korean Society of Water and Wastewater
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• v.23 no.5
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• pp.539-545
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• 2009

A feasibility of a pilot scale two-phase anaerobic digestion with ultra filtration system treating garbage leachate were evaluated. The treatment system consisted of a thermophilic acidogenic reactor, a mesophilic methanogenic reactor, and an UF membrane. The average COD removal efficiency of the treatment system was 95% up to the OLR of 3.1 g COD/L/d. The higher COD removal efficiency with membrane unit resulted from the removal of some portion of soluble organics by membrane as well as particulate materials. When the membrane unit was in operation, bulk liquid in acidogenic and methanogenic reactors was partially interchanged, which maintained the acidogenic reactor pH over 5.0 without external chemical addition. Also, with the production of methane in the acidogenic reactor, the organic loading rate of the methanogenic reactor reduced. The initial flux of the membrane unit was $50{\sim}60L/m^2/hr$, but decreased to $5 L/m^2/hr$ after 95 days of operation due to clogging caused by particulate materials such as fibrous materials in garbage leachate. To prevent clogging caused by particulate materials, a pretreatment system such as screening is required. With the improvement with membrane unit operation, the two-phase anaerobic digestion with ultra filtration system is expected to have the possibility of treating garbage leachate.

• Proceedings of the KIEE Conference
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• 1998.07f
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• pp.2175-2177
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• 1998

Sunlight makes it possible to adjust scale of electric power easily as a electric energy without air pollution. Solar cell to convert the sunlight to the electric energy has DC output which is influenced on temperature and irradiation time. Conversion of DC output from the solar cell to AC is necessary due to the fact that most loads to be used currently are compatible with AC generally. In the present work, Two-phase chopper system with two seperate groups to obtain two identical DC is used to preserve the energy from the solar cell in two battery. They are controlled to be operated around maximum output of the solar cell under the condition of constant voltage. Photovoltaic system with DC${\rightarrow}$AC conversion is also investigated for big capacity and two seperated electric power using two separate inverter.

• Journal of Power Electronics
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• v.16 no.6
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• pp.2243-2257
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• 2016

This paper presents a two stage three-phase proton exchange membrane fuel cell (PEMFC) generation system. When the system is connected to a three-phase load, it is very sensitive to the characteristics and type of the load. Especially unbalanced three-phase loads, which result in a pulsating power that is twice the output frequency at the inverter output, and cause the dc-link to generate low frequency ripples. This penetrates to the fuel cell side through the front-end dc-dc converter, which makes the fuel cell work in an unsafe condition and degrades its lifespan. In this paper, the generation and propagation mechanism of low frequency ripple is analyzed and its impact on fuel cells is presented based on the PEMFC output characteristics model. Then a novel method to evaluate low frequency current ripple control capability is investigated. Moreover, a control scheme with bandpass filter inserted into the current feed-forward path, and ripple duty ratio compensation based on current mode control with notch filter is also proposed to achieve low frequency ripple suppression and dynamic characteristics improvement during load transients. Finally, different control methods are verified and compared by simulation and experimental results.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.400-403
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• 2002

This paper presents a shearographic technique for measuring in-plane strains. During the measurement, the test object is illuminated alternately with two laser beams, symmetrically with respect to the viewing direction. Employing a phase shift technique, the phase distributions due to object deformation for each beam are obtained separately. The difference of the two phase distributions depicts the derivative of in-plane surface displacements. The technique is equivalent to a system of many strain gages.